Mobile or portable cellular telephones are typically arranged to communicate via a radio link to a base station of a network. Alternatively, a mobile telephone may communicate directly with a satellite.
Increasingly, cellular radio communications technology is being built into other devices. These include portable laptop ‘or notebook’ computers and ‘personal digital assistants’. These devices can then also send data or voice over cellular communications networks.
In future, practically any device may be able to communicate over a cellular communications network.
An analogous form of technology to the cellular telephone consists of digital portable and mobile radios with private networks. These are commonly referred to as ‘PMR’ radios. Portable and mobile radios may be arranged either to communicate with one another via base stations, or directly with one another in ‘direct mode’. The communication will typically either be over a digital simplex communication channel, or over a digital semi-duplex communication channel.
Mobile communications devices are commonly referred to as ‘mobile stations’. In the following, the term mobile station will be used to describe any such electronic device capable of transmission and reception of voice and/or data including cellular transceivers (both terrestrial and satellite) and radio pagers.
The next generation of mobile stations will operate in accordance with a standard referred to as the universal mobile telephone standard (UMTS). The UMTS infrastructure will offer varying levels of service for UMTS mobile stations.
One goal of UMTS is the efficient use of the bandwidth associated with the Imited radio spectrum available to system operators. Another goal is the orderly function of a variety of different levels of service offered by the network. A further goal is supporting a wide variety of UMTS mobile stations with varying capabilities. For example, whilst a UMTS cell might offer the possibility for a mobile station to transmit video imagery, many mobile stations operating within that cell may not be capable of transmitting or receiving video imagery.
In cellular telecommunication systems, such as GSM and UMTS, the 25 broadcast capacity is limited for a number of different reasons. In the case of GSM, the original system design makes it difficult to extend the control channel overheads specified with the existing standard. The broadcast channels use spectrum for non-chargeable purposes. This may be seen as undesirable by an operator. The problem of broadcast capacity is a particular problem for multi-mode systems, in which there is a need to broadcast information about several modes, thus utilising significant amounts of the bandwidth allocation.